Renal ANATOMY

Presenter: Yusuf Abdirisak Mohamed

13th March 2017

Bean shaped Weight Females 135gMales 150gPoles,

surfaces, borders & hilum

Kidney Position• The left kidney is related to ribs 11 and 12. Its upper pole is located at

vertebral level T11, and it is also located higher than the right kidney.• • The right kidney is only related to rib 12. Its upper pole is located at

T12. The presence of the liver is the reason the right kidney is lower down.

• • The kidneys are retroperitoneal organs, which lie on the ventral

surface of the quadratus lumborum muscle, lateral to the psoas muscle and vertebral column, and superior to the iliacus.

Kidney• Each kidney has a thick outer cortex, surrounding a medulla that is

divided into 8 to 12 renal pyramids; each pyramid and its associated cortical tissue comprises a renal lobe.

• The apical papilla of each renal pyramid inserts into a minor calyx, a subdivision of two or three major calyces extending from the renal pelvis.

• The ureter carries urine from the renal pelvis and exits the renal hilum, where the renal artery and vein are also located.

• Striations extending from the medulla into the cortex are called medullary rays; these plus the attached cortical tissue are considered lobules.

STRUCTURE OF THE KIDNEY • The specific components of the kidney are the nephrons,

the collecting ducts, and a unique microvasculature.

• The multipapillary kidney of humans contains about 1 million nephrons, although this number varies considerably.

• The number of nephrons is already established during prenatal development; afer birth, new nephrons cannot be developed, and a lost nephron cannot be replaced.

Nephrons • A nephron consists of a renal

corpuscle (glomerulus) connected to a complicated and twisted tubule that finally drains into a collecting duct

• There are two types of nephron, those with long loops of Henle and those with short loops.

• Short loops turn back in the outer medulla or even in the cortex (cortical loops).

• Long loops turn back at successive levels of the inner medulla.

Collecting Ducts • A collecting duct is formed in the renal cortex when

several nephrons join. A connecting tubule is interposed between a nephron and a cortical collecting duct.

• Cortical collecting ducts descend within the medullary rays of the cortex. These ducts traverse the outer medulla as unbranched tubes.

• On entering the inner medulla, the cortical collecting ducts fuse successively and open finally as papillary ducts into the renal pelvis

Microvasculature • The renal artery, after entering the renal sinus, finally

divides into the interlobar arteries, which extend toward the cortex in the space between the wall of the pelvis (or calyx) and the adjacent cortical tissue

• At the junction between cortex and medulla, the interlobar arteries divide and pass over into the arcuate arteries, which also branch. The arcuate arteries give rise to the cortical radial arteries (interlobular arteries), which ascend radially through the cortex. No arteries penetrate the medulla.

•

• Glomeruli are drained by efferent arterioles. Two basic types of efferent arterioles can be distinguished, cortical and juxtamedullary.

• Cortical efferent arterioles, which derive from superficial and mid- cortical glomeruli, supply the capillary plexus of the cortex.

• The efferent arterioles of juxtamedullary glomeruli represent the supplying vessels of the renal medulla

NEPHRON Renal Glomerulus (Renal Corpuscle) •The glomerulus comprises a tuft of specialized capillaries attached to the mesangium, both of which are enclosed in a pouch-like extension of the tubule, the glomerular capsule, or Bowman capsule.

• The capillaries and mesangium are covered by epithelial cells (podocytes), forming the visceral epithelium of Bowman capsule.

• At the interface between the glomerular capillaries and the mesangium on one side and the podocyte layer on the other side, the glomerular basement membrane (GBM) develops.

• The space between both layers of Bowman capsule represents the urinary space, which at the urinary pole continues as the tubule lumen.

• Glomerular capillaries are a unique type of blood vessel consisting of only an endothelial tube

• The major components of the GBM include type IV collagen, laminin, and heparan sulfate proteoglycans, as in basement membranes at other sites.

• Types V and VI collagen and nidogen (entactin) have also been demonstrated. However, the GBM has several unique properties, notably a distinct spectrum of type IV collagen and laminin isoforms.

• The mature GBM consists of type IV collagen made of α3, α4, and α5 chains (instead of α1 and α2 chains of most other basement membranes) and laminin 11, made of α5, β2, and γ1 chains

• Type IV collagen is the antigenic target in Goodpasture disease

• Mutations in the genes of the α3, α4, and α5 chains of type IV collagen are responsible for Alport syndrome

Mesangium

• Three major cell types occur within the glomerular tuft , all of which are in close contact with the GBM: mesangial cells, endothelial cells, and podocytes.

• The mesangial/endothelial/podocyte cell ratio is 2 : 3 : 1 in the rat.

Mesangial Cells Mesangial cells are irregular in shape, with many

processes extending from the cell body toward the GBM

Endothelium •Glomerular endothelial cells consist of cell bodies and peripherally located, attenuated, and highly fenestrated cytoplasmic sheets. •Glomerular endothelial pores lack diaphragms, which are encountered only in the endothelium of the final tributaries to the efferent arteriole

Visceral Epithelium (Podocytes) •The visceral epithelium of Bowman capsule comprises highly differentiated cells, the podocytes •In the developing glomerulus, podocytes have a simple polygonal shape. •The most specific structural feature of podocytes is the pattern of foot processes covering the outer aspect of glomerular capillaries

Renal Tubule • The renal tubule is

subdivided into several distinct segments: a proximal tubule, an intermediate tubule, a distal tubule, a connecting tubule (CNT), and the collecting duct

• The renal tubules are outlined by a single-layer epithelium anchored to a basement membrane.

Proximal Tubule • The proximal tubule reabsorbs the bulk of filtered water

and solutes • The proximal tubule has a prominent brush border

(increasing the luminal cell surface area) and extensive interdigitation by basolateral cell processes (increasing the basolateral cell surface area).

Loop of Henle

• The loop of Henle consists of the straight portion of the proximal tubule, thin descending limb and (in long loops) thin ascending limb, and thick ascending limb

Distal Convoluted Tubule • The epithelium is quite highly differentiated, exhibiting the

most extensive basolateral interdigitation of the cells and the greatest density of mitochondria in all nephron portions .

• Apically, the cells are equipped with numerous microvilli.

COLLECTING DUCT SYSTEM • The collecting ducts may be subdivided into cortical and

medullary ducts, and the medullary ducts into outer and inner

• As with the CNT, the collecting ducts are lined by two types of cell: CD cells (principal cells) and IC cells

• The CD cells are simple, polygonal cells increasing in size toward the tip of the papilla

• The second cell type, the IC cell, is present in both the CNT and the collecting duct

JUXTAGLOMERULAR APPARATUS • The juxtaglomerular apparatus comprises the macula

densa, the extraglomerular mesangium, the terminal portion of the afferent arteriole with its renin-producing granular cells (also ofen termed juxtaglomerular cells), and the beginning portions of the efferent arteriole

• The macula densa is a plaque of specialized cells in the wall of the thick ascending limb of Henle at the site where the limb attaches to the extraglomerular mesangium of the parent glomerulus

RENAL INTERSTITIUM • The interstitium of the kidney is comparatively sparse. Its fractional volume

in the cortex ranges from 5% to 7%, with a tendency to increase with age.

• Renal interstitium increases across the medulla from cortex to papilla. In the outer stripe, it is 3% to 4%, the lowest value of all kidney zones; this is interpreted as forming a barrier to prevent loss of solutes from a hyperosmolar medulla into the cortex.

• Renal interstitium is 10% in the inner stripe and up to about 30% in the inner medulla.

• The cellular constituents of the interstitium include resident fibbroblasts, which establish the scaffold frame for renal corpuscles, tubules, and blood vessels, as well as varying numbers of migrating cells of the immune system, especially dendritic cells.

Ureter• The ureters are lined by urothelium, or transitional epithelium, which

protects underlying cells from hypertonic or toxic effects of urine.

• Large, bulbous superficial cells of the urothelium, called umbrella cells, have apical membranes consisting of hinged regions with dense plaques of uroplakin proteins.

• Characteristic pattern of longitudinally folded mucosa, surrounded by a thick muscularis that moves urine by regular waves of peristalsis.

Inner longitudinal and outer circular muscles

Bladder• Urothelium is surrounded by a folded lamina propria and submucosa,

followed by a dense sheath of interwoven smooth muscle layers and adventitia

• The bladder's lamina propria and dense irregular connective tissue of the submucosa are highly vascularized.

• As the urinary bladder fills its highly folded mucosa unfolds, the urothelium gets somewhat thinner by cell movements, and the hinged membrane plaques of umbrella cells partially unfold.

• The muscularis consists of three poorly delineated layers, collectively called the detrusor muscle

• All the urinary passages are covered externally by an adventitial layer, except for the upper part of the bladder that is covered by serous peritoneum.

Urethra• The urethra drains the bladder and is lined by unusual stratified

columnar and pseudostratified columnar epithelium.

• In males the urethra has three regions: the prostatic urethra in the prostate gland; the short membranous urethra passing through the urogenital diaphragm, and the long penile urethra.

• In women, the urethra is 4- to 5-cm-long, lined initially with transitional epithelium, then by stratified squamous epithelium and some areas of pseudostratified columnar epithelium

Divisions of the Urethra• Preprostatic urethra• Prostatic Urethra• Membranous Urethra • Bulbous Urethra • Spongy Urethra• Distal Penile Urethra

Visceral Pain of the Pelvic Region• Kidneys

• T12-L2 dermatomes

• Proximal ureter• Renal plexus + abdominal aortic plexus

• Middle ureter• L1-L2

• Distal ureter• L3-L4

• Bladder• S2-S4, T11-L2

Renal Transplantation

Refences• COMPREHENSIVE CLINICAL NEPHROLOGY 5th ED

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